[PATCH] mt76: fix tx status related use-after-free race on station removal

Felix Fietkau
2022-04-23T05:17:00Z

There is a small race window where ongoing tx activity can lead to a skb
getting added to the status tracking idr after that idr has already been
cleaned up, which will keep the wcid linked in the status poll list.
Fix this by only adding status skbs if the wcid pointer is still assigned
in dev->wcid, which gets cleared early by mt76_sta_pre_rcu_remove

Fixes: bd1e3e7b693c ("mt76: introduce packet_id idr")
Tested-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
drivers/net/wireless/mediatek/mt76/mac80211.c | 2 ++
drivers/net/wireless/mediatek/mt76/tx.c | 2 +-
2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mac80211.c b/drivers/net/wireless/mediatek/mt76/mac80211.c
index 2dd3ebd1863f..8a2fedbb1451 100644
--- a/drivers/net/wireless/mediatek/mt76/mac80211.c
+++ b/drivers/net/wireless/mediatek/mt76/mac80211.c
@@ -1381,7 +1381,9 @@ void mt76_sta_pre_rcu_remove(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
struct mt76_wcid *wcid = (struct mt76_wcid *)sta->drv_priv;

mutex_lock(&dev->mutex);
+ spin_lock_bh(&dev->status_lock);
rcu_assign_pointer(dev->wcid[wcid->idx], NULL);
+ spin_unlock_bh(&dev->status_lock);
mutex_unlock(&dev->mutex);
}
EXPORT_SYMBOL_GPL(mt76_sta_pre_rcu_remove);
diff --git a/drivers/net/wireless/mediatek/mt76/tx.c b/drivers/net/wireless/mediatek/mt76/tx.c
index c3be62f58b62..d5a8456c108b 100644
--- a/drivers/net/wireless/mediatek/mt76/tx.c
+++ b/drivers/net/wireless/mediatek/mt76/tx.c
@@ -120,7 +120,7 @@ mt76_tx_status_skb_add(struct mt76_dev *dev, struct mt76_wcid *wcid,

memset(cb, 0, sizeof(*cb));

- if (!wcid)
+ if (!wcid || !rcu_access_pointer(dev->wcid[wcid->idx]))
return MT_PACKET_ID_NO_ACK;

if (info->flags & IEEE80211_TX_CTL_NO_ACK)
--
2.35.1